1. Field
Embodiments of the claimed invention relate to optical measurements, and in particular, an apparatus and method for making optical measurements of samples.
2. Description of Related Art
Spectrometers are instruments used to measure the optical properties of light traveling through samples. These measurements can be used for a variety of purposes, such as to identify materials. Spectrometers typically include an upper arm having a first measurement surface coupled to a lower arm having a second measurement surface via a hinge. One of the measurement surfaces is coupled to a light source, while the other is coupled to a detector.
Two opposing fiber optic cables are provided on the opposing measurement surfaces. A sample is placed on the tips of the fiber optic cables of the lower measurement surface, and the upper measurement surface is brought into contact with the sample. The sample is pulled into a column by slightly moving the lower measurement surface and the upper measurement surface away from each other. Transmittance or absorbance of light is then measured through the sample at different distances of the upper measurement surface and the lower measurement surface.
Conventionally, the distance between the two measurement surfaces is controlled by a screw that protrudes from the base of the spectrometer. The screw comes in direct contact with the upper arm upon which the upper measurement surface is positioned. Thus, when the screw is moved up or down, the upper arm is directly moved up or down.
However, other methods of controlling the distance between the two measurement surfaces have been employed. U.S. Pat. No. 7,969,575 B2 to Zuo discloses an apparatus for measuring light absorption of liquid samples including an actuator configured to position the upper arm into a first measuring position. The actuator includes a step motor and a pushing rod, which when the step motor rotates, the pushing rod is moved linearly up and down. When extended upwardly, the pushing rod pushes a pushing pin, which in turn pushes another pin in the upper arm, which in turn pushes the upper arm upwardly. This positions the measuring surfaces at a particular distance apart.
U.S. Pat. No. 8,189,199 to Robertson, Jr. et al. relates to a dual sample mode spectrophotometer that selectively measures samples in either a vessel or as a surface tension retained sample held between two opposing pedestals. A lower optical fiber connector translates along the vertical direction to enable the spacing between the two optical fibers to be varied. The base plate is provided with a linear actuator that is mounted thereto so as to provide for precise movement of the lower optical fiber connector. The linear actuator comprises a motor designed to produce a rotational motion of a threaded nut which bears on a mating threaded shaft portion of the lower optical fiber holder. The rotation of the internally threaded screw against the externally threaded shaft portion causes controlled movement of the lower fiber optic connector.